1. Field of the Invention
The present invention relates generally to an access transistor used to access memory and method of fabricating the same, and more particularly to an access transistor with a small form factor.
2. Description of the Prior Art
Magnetic random access memory (MRAM) is rapidly gaining popularity as its use in replacing conventional memory is showing promise. Magnetic tunnel junctions (MTJs), which are essentially the part of the MRAM that store information, include various layers that determine the magnetic behavior of the device. An MTJ is typically formed with an accompanying access transistor used to select (or access) the MTJ for programming and/or reading. The MTJ and access transistor are herein referred to as a “magnetic memory cell”. Currently, the size of such a combination is typically 14 F2, with “F” representing feature size. Such a form factor prevents magnetic memory cells from readily replacing other memory, such as dynamic random access memory (DRAM), which is typically 6 F2 and NAND flash memory, which is typically 4 F2. For the benefits experienced by magnetic memory cells, such as long life expectancy and avoidance of the limitations currently experienced with fabrication of silicon-based memory, it is highly desirable to manufacture magnetic memory cells that resemble a form factor similar to that of DRAM so that the latter can be replaced by the former.
One of the reasons for current magnetic memory cell's large sizes is the formation of the access transistor. Currently, access transistors are formed horizontally, relative to the plane of the silicon substrate, beside and under the MTJ. Such a configuration limits efficient use of the surface of the silicon substrate and results in a large memory cell size.
Current prior art technology uses 6 F2 perpendicular Spin Torque (PST) MRAM cell. Problems with the memory cell includes low drive current, the current required to effectively access the MTJ, punch through leakage due to the short channel and lack of sufficient space for making contact in between.
Thus, the need arises for reducing the size of an access transistor.